The flight of an aircraft can be modified using flight control surfaces that are connected to the aircraft's wing. The control surfaces include ailerons, flaps, and spoilers that can be used to roll the aircraft, provide additional lift, or control an airspeed of the aircraft.
Flaps are surfaces that are mounted at the trailing edge of each wing. During high-speed flight, the flaps are retracted underneath the wing and do not usually contribute significantly to the aerodynamic characteristics of the wing. During low speed flight, however, the flaps can be deployed from the trailing edge of the wing to modify the shape of the wing to increase lift.
Generally, the flaps increase the wing's camber—the degree of asymmetry between the top surface and bottom surface of the wing. Although deployed flaps create drag, the flaps can be used during take-off or landing to increase lift and to allow for flight at slow speed. In some aircraft, the flaps are deployed on a rail or track system, also referred to as a flap track that allows the flaps to extend away from the trailing edge of the wing, thereby increasing both the wing's camber and surface area. In such an implementation, the flaps can be fixed to a shuttle that runs along the rail or track system, changing a position of the flaps. Because the flaps are fixed to the shuttle, the flaps cannot be articulated and cannot be used as control surfaces to roll or bank the aircraft. Instead, those actions are implemented using ailerons.
An aileron is a hinged panel on the trailing edge of the wing, usually located at the outboard portion of the wing. The aileron can either be raised or lowered to decrease or increase lift on the wing. When deflected downwardly, the aileron increases the lift of the wing, to roll or bank the airplane into a turn. At the same time, the aileron on the other wing is deflected upwardly, to decrease the lift on that wing to augment the rolling motion.
One of the most objectionable features of conventional aileron applications is a phenomenon referred to as “adverse yaw.” When a turn is initiated with conventional ailerons, the nose of the airplane turns first in a direction opposite to that of the intended turn. This is usually compensated for by using rudder deflection to coordinate the turn. The adverse yawing motion is a direct result of aileron application. While producing more lift to bank the airplane into a turn, the downwardly-deflected aileron also produces more drag, which acts initially to cause the airplane's nose to turn in the direction opposite to the intended turn. That is, when one wing is lifted relative to the other wing by operation of a conventional aileron to bank the airplane into a turn, it is also pulled back away from the turn relative to the wing on the other side, causing the nose initially to turn, or yaw, in the direction opposite to the turn. This effect becomes increasingly detrimental as the roll rate increases and/or airspeed decreases.
In addition to resulting in inefficient flight, adverse yaw produced by the conventional aileron often contributes to spin entry. When spinning, an airplane is descending and turning in a tight spiral flight path. In a left hand spin, for example, the left wing is down and toward the center of the spiral. Instinctively, many pilots are tempted to initiate right stick or control yoke movement to roll towards the right and out of the spin. With conventional ailerons this action deploys the left aileron down and the right aileron up. The left aileron creates more drag and the spin will be further aggravated.
Another disadvantage of conventional ailerons is that they also require commitment of a sizable portion of the trailing edge of the wing that could otherwise be used for beneficial high-lift devices such as flaps that would otherwise allow lower approach, landing and takeoff speeds—especially advantageous for heavy, high-speed commercial and high-performance military aircraft. Because conventional ailerons and conventional flaps are considered as having separate functions, different regions of the trailing edge of a wing are separately used for either aileron or flap placement.
In view of the draw-backs of conventional aileron and flap configurations, an improved aircraft aileron system has been developed. The improved aileron system is described in U.S. Pat. No. 6,079,672 to Lam, et al. and U.S. Pat. No. 6,554,229 to Lam, et al. and includes two independent panels located at the rear portion of the wing as described in the referenced U.S. Patents. The panels are located in a span-wise direction and aligned with the wing's trailing edge. The panels are independently hinged at their leading edges and are configured to rotate to create angular deflections with respect to the wing. The upper panel (the “aileron panel”) may be restricted to upward deflection only from its neutral position and in operation is deployed independently as an aileron. The lower panel (the “flap panel”) is capable of both upward and downward deflections from its neutral position, and is deployed independently downward as an auxiliary flap. Both panels are deployed together upwardly only as an aileron. Alternatively, the lower auxiliary flap panel is capable of downward deployment only, to provide a simpler aileron system. For roll control of an aircraft during cruise, one or both of the ailerons panels on one side only are deflected upwards while the aileron panels on the other side remains in its neutral position, as described in the U.S. Patent.
Although there exists shuttle and track systems for extending conventional flap structures, the systems serve a fixed flap that cannot be upwardly deflected to act as a functional component in a dual-panel aileron system. Because conventional flaps cannot be so articulated, conventional flaps are generally fixed solidly to the shuttle to restrict the movement of the flaps to that which is allowed by the track. As such, the flaps can only be extended or retracted along the track—no other articulation is possible. Accordingly, there exists a need for a flap panel shuttle for use in dual-panel aileron systems, wherein the lower panel of the dual-panel aileron system may be configured to operate as a flap and the shuttle is configured to either extend the flap panel along a track system, or allow the flap panel to be articulated upwards with an aileron panel.